محاسبۀ ضخامت كمينۀ حفاظ براي اتاق ماموگرافي به‌كمك كد MCNP-4C

The least shielding design requirements for a mammography room using MCNP-4C code

In this study MCNP-4C code is used to simulate the least shielding requirements for a mammography room. In order to simulate the X-ray tube, a molybdenum target is irradiated by 28 keV electrons. Then, a molybdenum filter with a thickness of 30 micrometers was used to remove the low-energy parts of X-ray spectrum. Finally the dosimetry evaluations were conducted after designing the lead shield of the X-ray tube and considering the default minimum thickness of the gypsum walls, concrete floor and ceiling that more often is expected in most buildings. Accordingly, 8.976 mrems/h was obtained as a result of simulation by the MCNP-4C code at a distance of 5 cm from the lead shield with 0.05 cm thickness. This amount of dose rate is substantially fewer than the maximum safe value of 100 mrems/h reported by the NCRP. Moreover, the dose rates calculated for the walls, floor and ceiling of the mammography room were obtained1.03e-02, 1.463E-02 and 6.476e-03 mrems/h respectively, that are fewer than the maximum safe amount of 5e-02 mrems/h. Therefore the results clearly indicate that extra shielding consideration is not required due to influence of the low X-ray energies used in mammography equipment.